The present invention relates to a water-swellable composition and a leakage-preventing material therewith capable of swelling by absorbing water and preventing leakage of water by clogging or filling interstices.
In public works and civil engineering construction works, cracks, cleavages or interstices often form in the places where mortar or concrete has been placed or wherein water-supplying pipes are jointed, and not rarely make a cause of leakage of water. In the prior art, such cracks or interstices are filled with a leakage-preventing material based on rubber, plastics and bitumen, such as rubber packing materials, rubber sealants and bitumen jointing materials. During the use for a long period of time, there may sometimes take place resumed leakage of water in the place due to the deterioration of the leakage-preventing material per se or change in size of the interstices filled with the material. A leakage-preventing material based on a water-swellable polymeric composition has been proposed which can be swelled with the passing out water and can more tightly fill the interstices. Leakage-preventing materials of this type are effective in overcoming the above mentioned drawbacks of the traditional materials of mere caulking type if the water-swellable material has a sufficiently high swelling ratio as well as a high mechanical strength of the swollen gel.
As an example of such a type of water-swellable polymeric compositions, there have been disclosures in the U.S. Pat. Nos. 4,155,957 and 4,211,851, according to which the polymer composition comprises a copolymer of a lower olefin and maleic anhydride, an aqueous emulsion of an acrylic polymer having compatibility with the above copolymer and a compound having, in a molecule, at least two functional groups selected from the class consisting of hydroxy, amino and epoxy groups.
The above described water-swellable polymeric composition or leakage-preventing material is indeed effective to be swelled with water and to exhibit the desired effect when the ionic strength of the water coming into contact therewith is low or, in other words, the water contains very little amounts of electrolyte materials dissolved therein. When the water contains considerable amounts of cations of, for example, sodium, calcium, iron and the like, on the other hand, the polymeric composition can be swelled only insufficiently or sometimes dissolved in the water so that no satisfactory effect of leakage prevention is obtained.